System and method for recycling high-boiling-point waste photoresist stripper

ABSTRACT

This invention relates to a system and method for recycling a high-boiling-point waste photoresist stripper generated in processes of manufacturing LCDs or semiconductor devices, wherein an expensive high-boiling-point stripper solvent can be easily recycled at high yield and high-purity electronic grade. This system includes a first distillation device for removing low-boiling-point impurities, a second distillation device for recycling a stripper solvent composition while removing high-boiling-point impurities, and a third distillation device for removing trace water, thus recovering the stripper solvent composition, and further includes a fourth distillation device for additionally recycling a stripper solvent, thus additionally recovering a high-boiling-point stripper solvent, and this method includes removing low-boiling-point impurities, recycling a stripper solvent composition while removing high-boiling-point impurities, and removing trace water, thus recovering the stripper solvent composition, and further includes additionally recycling a stripper solvent.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of KoreanPatent Application Nos. 10-2013-019743 filed on Feb. 25, 2013, and10-2013-0023760 filed on Mar. 6, 2013, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for recycling ahigh-boiling-point waste photoresist stripper, and more particularly, toa system and method for recycling a high-boiling-point waste photoresiststripper, wherein an expensive high-boiling-point stripper solvent maybe easily recycled at high yield and in the level of high-purityelectronic grade from a high-boiling-point waste photoresist strippergenerated in a process of manufacturing a liquid crystal display or asemiconductor device.

2. Description of the Related Art

With the drastic advancement of information communication industries,the demand for electronic devices and liquid crystal displays (LCDs)using a variety of semiconductor devices is continuously increasing.Accordingly, a photoresist, which is a key to the formation of amicropattern of a wafer and a circuit board, and an expensive stripperfor dilution and removal of such a photoresist are increasinglyrequired, and furthermore, the need for recycling such a stripper usedis on the rise.

For example, a waste stripper is mainly generated during a photo processfor forming a circuit pattern in the course of manufacturing electronicparts such as semiconductor wafers, LCDs, glass substrates, etc., andthe waste stripper contains not only stripper solvents but also aphotoresist resin, water, impurities such as heavy metals, etc.

The waste stripper is mostly removed by way of incineration or landfillafter simple pre-treatment, but may cause environmental problems andtreatment cost problems from generation of the waste to removal thereof.Ultimately, competitiveness of IT industries may become weakened andthus ensuring resources through recycling of waste solvents is urgentlyrequired.

As electronic parts and devices combined with IT technology have beenrapidly developed, kinds or functions of thinner and stripper used inthe manufacturing processes have become diversified. Nevertheless, theamounts of main stripper solvents which are reused through recovery andpurification after having been used for processes of manufacturingelectronic parts such as TET-LCD (which is an ultrathin film liquidcrystal display), etc. are very small at the present time.

Particularly in TET-LCD fields, substrates are large-sized and panelprices are falling, and thus the demand for processing cost savings isincreasing. Under circumstances in which high prices of raw materials ofthinners and strippers result from the recent rise in oil prices, costcompetitiveness has to be ensured. Hence, when waste strippers areutilized again as raw materials through purification, the use of rawmaterials is reduced, and also, environmental problems which become moreserious and treatment cost problems may be solved.

Extensive research to recycling techniques of the waste in a strippingprocess is ongoing these days in terms of economy, environment andefficiency. In regard to a waste stripper recycling technique, KoreanPatent No. 0901001 and Japanese Patent Application Publication No.2005-288329 disclose a technique for recycling a stripper solvent byremoving a low-boiling-point material such as water, etc. and ahigh-boiling-point material such as a photoresist resin, etc., from thewaste stripper, and Korean Patent No. 0899777 discloses a high-yieldrecycling method in which the recycling loss is minimized.

However, due to the recent advancement of LCD and semiconductorindustries, a new type photoresist resin is being used depending on thedevelopment of a novel memory semiconductor, and a highly functionalstripper organic solvent is required to easily dissolve the photoresistresin in the course of stripping the photoresist resin during themanufacturing process. Although the use of high-boiling-point strippersolvents having high stripper solubility is increasing, limitations areimposed on recycling the high-boiling-point stripper solvents using therecycling method as above.

In the recycling method as above, because of high-boiling-pointproperties, including high viscosity, thermal decomposition and colorchange, the high-boiling-point stripper organic solvents are difficultto separate and purify from heavy photoresist resin and metalcomponents, and are allowed to excessively remain in order to preventgeneration of processing difficulties, and then discarded together withhigh-boiling-point impurities.

Also, the recovery efficiency of high-boiling-point stripper organicsolvents recovered by the conventional recycling methods approximates to15%, which is regarded as economically insignificant. The qualityincluding purity and color of the recovered high-boiling-point strippersolvents is poor and thus the recycling value thereof is low, which isundesirable.

The demand for techniques for recycling and recovering of expensivehigh-boiling-point stripper organic solvents is being agitated in therelated industries, but there are still no alternatives to the recyclingtechniques at home and abroad.

Hence, there is an urgent need to secure advanced recycling techniquesable to recover expensive high-boiling-point stripper organic solventsthrough recycling and purification from a photoresist residue which isbeing discarded, in addition to the typical stripper organic solvent ofthe waste photoresist stripper. If a high-boiling-point stripper solventwhich is an expensive valuable resource completely imported from abroadis recovered in a large amount at high recovery efficiency and thenreused, efficient energy management and competitiveness of IT relatedcompanies are likely to remarkably increase, and more practicalenvironmental improvement effects are expected.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made keeping in mind theproblems encountered in the related art, such as low recycling yield ofa high-boiling-point stripper solvent, and an object of the presentinvention is to provide a system for recycling a high-purity electronicgrade high-boiling-point stripper solvent from a high-boiling-pointwaste photoresist stripper, which includes a first distillation devicefor removing low-boiling-point impurities from a high-boiling-pointwaste photoresist stripper generated in processes of manufacturing LCDsor semiconductor devices, a second distillation device for recycling astripper solvent composition while removing high-boiling-pointimpurities, and a third distillation device for removing trace water tothus recover the stripper solvent composition, and also further includesa fourth distillation device for additionally recycling a strippersolvent, and thus a high-boiling-point stripper solvent discarded as adistillation residue together with the high-boiling-point impurities maybe additionally recovered, thereby greatly increasing the recyclingyield of the expensive high-boiling-point stripper solvent.

Another object of the present invention is to provide a method ofrecycling a high-purity electronic grade high-boiling-point strippersolvent from a high-boiling-point waste photoresist stripper, whichincludes removing low-boiling-point impurities from a high-boiling-pointwaste photoresist stripper generated in the processes of manufacturingLCDs or semiconductor devices, recycling a stripper solvent compositionwhile removing high-boiling-point impurities, and removing trace waterto thus recover the stripper solvent composition, and also furtherincludes additionally recycling a stripper solvent, and thus ahigh-boiling-point stripper solvent discarded as a distillation residuetogether with the high-boiling-point impurities may be additionallyrecovered, thereby greatly increasing the recycling yield of theexpensive high-boiling-point stripper solvent.

In order to accomplish the above objects, the present invention providesa system for recycling a high-boiling-point waste photoresist stripper,comprising a first distillation device, a second distillation device anda third distillation device, which are disposed in a line to performtotal stripper recycling of a pretreated high-boiling-point wastephotoresist stripper, the first distillation device for removinglow-boiling-point impurities from the high-boiling-point wastephotoresist stripper, the second distillation device for removinghigh-boiling-point impurities from the high-boiling-point wastephotoresist stripper without the low-boiling-point impurities andsimultaneously recovering a stripper solvent composition, and the thirddistillation device for removing trace water from the stripper solventcomposition without the high-boiling-point impurities; and a fourthdistillation device connected to an outlet of the second distillationdevice and disposed adjacent thereto to perform additional stripperrecycling for additionally recovering a high-boiling-point strippersolvent from a high-boiling-point residue including thehigh-boiling-point impurities discharged after having been removed bythe second distillation device.

Also in the present invention, a fifth distillation device is furtherdisposed, which is connected to outlets of the second distillationdevice and the fourth distillation device to perform separate stripperrecycling for separately recovering, as individual high-purity recycledstrippers, the stripper solvent composition recovered by the seconddistillation device and the high-boiling-point stripper solventadditionally recovered by the fourth distillation device.

In an exemplary embodiment of the present invention, the firstdistillation device comprises a distillation tower, which has 15˜25theoretical plates for purification and receives the pretreatedhigh-boiling-point waste photoresist stripper; a reboiler connected to abottom of the distillation tower and set to a temperature of 80° C. orless so as to heat the waste stripper transported to the distillationtower to evaporate the low-boiling-point impurities; a condenserconnected to a top of the distillation tower so as to condense theextracted low-boiling-point impurities; a temporary storage tankconnected to the condenser so that the low-boiling-point impuritiescondensed by the condenser are temporarily stored; a second transportpump and a separate collection tank connected side by side to an outletof the temporary storage tank to discharge the low-boiling-pointimpurities recovered in the temporary storage tank; and a thirdtransport pump connected to an outlet of the reboiler to transport thewaste stripper without the low-boiling-point impurities to the seconddistillation device.

Also, a vacuum pump may be connected to a top of the temporary storagetank to reduce an inner pressure of the distillation tower so thatvacuum operation is carried out, in order to prevent promotion ofthermal decomposition when the high-boiling-point waste stripper in thedistillation tower of the first distillation device is heated.

In an exemplary embodiment of the present invention, the seconddistillation device comprises a distillation tower, which has 7˜15theoretical plates for purification and receives the waste strippertransported from the reboiler of the first distillation device; areboiler connected to a bottom of the distillation tower and set to atemperature of 160° C. or less so as to heat the waste strippertransported to the distillation tower to evaporate the stripper solventcomposition; a condenser connected to a top of the distillation tower soas to condense the extracted stripper solvent composition; a temporarystorage tank for temporarily storing the stripper solvent compositionrecovered after having been condensed by the condenser; and a fifthtransport pump and a sixth transport pump connected side by side to anoutlet of the temporary storage tank so that the stripper solventcomposition recovered in the temporary storage tank is transported tothe third distillation device.

Also, a vacuum pump may be connected to a top of the temporary storagetank to reduce an inner pressure of the distillation tower so thatvacuum operation is carried out, in order to prevent promotion ofthermal decomposition when a stripper solvent component contained in thewaste stripper in the distillation tower of the second distillationdevice is heated.

In an exemplary embodiment of the present invention, the thirddistillation device comprises a distillation tower, which has 25˜35theoretical plates for purification and receives the stripper solventcomposition obtained by the second distillation device; a reboilerseparately connected to a bottom of the distillation tower and set to atemperature of 110° C. or less to remove trace water from the strippersolvent composition transported to the distillation tower; a condenserconnected to a top of the distillation tower so that the removed tracewater and volatiles are condensed to be re-circulated to the firstdistillation device; an additional condenser connected to the top of thedistillation tower so as to condense a part of the stripper solventwhich is volatilized from the top of the tower; a temporary storage tankfor temporarily storing the part of the stripper solvent condensed bythe additional condenser; and an eighth transport pump for finallytransporting the stripper solvent in the temporary storage tank and theremaining stripper solvent in the bottom of the distillation tower andthe reboiler, to a recycled stripper mixture storage tank.

Also, a vacuum pump may be connected to a top of the temporary storagetank to reduce an inner pressure of the distillation tower so thatvacuum operation is carried out, in order to prevent promotion ofthermal decomposition when a stripper solvent component contained in thewaste stripper in the distillation tower of the third distillationdevice is heated.

In an exemplary embodiment of the present invention, the fourthdistillation device comprises a temporary storage tank for temporarilystoring a waste byproduct which is a high-boiling-point residue leftbehind in the bottom of the tower of the second distillation device andthe reboiler; a distillation tower, which has 8˜12 theoretical platesfor purification and receives the waste byproduct in the temporarystorage tank by actuation of a ninth transport pump; a reboilerseparately connected to a bottom of the distillation tower and set to atemperature of 160° C. or less so as to heat the waste byproducttransported to the distillation tower to evaporate the stripper solventcomposition; a condenser connected to a top of the distillation tower soas to condense the stripper solvent volatilized from the wastebyproduct; a temporary storage tank for recovering and temporarilystoring the condensed stripper solvent; and a twelfth transport pump anda thirteenth transport pump connected to an outlet of the temporarystorage tank so as to transport the recovered stripper solvent to therecycled stripper mixture storage tank.

Also, a vacuum pump may be connected to a top of the temporary storagetank to reduce an inner pressure of the distillation tower so thatvacuum operation is carried out, in order to prevent promotion ofthermal decomposition when a high-boiling-point stripper solventcomponent of the waste byproduct in the above distillation tower isheated.

In a further exemplary embodiment of the present invention, the fourthdistillation device further comprises, as control members for maximallyincreasing a recycling yield of the stripper solvent composition whilemaximally retarding deposition of a photoresist resin, a viscometer formonitoring an extent of viscosification of the high-boiling-pointstripper solvent contained in the high-boiling-point residue when thephotoresist resin, which is not sufficiently concentrated, of the wastebyproduct in the reboiler is transported to an impurity collection tankand discarded; a first flow rate control valve disposed together with atenth transport pump in a circulation line upwards from an outlet of thereboiler; a second flow rate control valve disposed together with aneleventh transport pump in a connection line between the outlet of thereboiler and the collection tank; and a controller for controllingopening/closing of the first and second flow rate control valvesdepending on measurement results of the viscometer.

In an exemplary embodiment of the present invention, the fifthdistillation device comprises a spiral spinning band type distillationtower including therein a spiral stirring type column device made ofmetal or Teflon so that the stripper solvent composition recoveredthrough the second removal step using the second distillation device,and the high-boiling-point stripper solvent recovered using the fourthdistillation device are recovered as individual high-purity electronicgrade recycled stripper solvents depending on a boiling point.

In an exemplary embodiment of the present invention, a 1-micron filteris disposed in a connection line between the outlet of the temporarystorage tank of the third distillation device and the recycled strippermixture storage tank, and in a connection line between an outlet of thefifth distillation device and individual stripper solvent storage tanks.

In addition, the present invention provides a method of recycling ahigh-boiling-point waste photoresist stripper, comprising pretreatingthe high-boiling-point waste photoresist stripper to remove a solid, aninsoluble denatured photoresist component and an organic acid componenttherefrom; subjecting the pretreated high-boiling-point wastephotoresist stripper to total stripper recycling including a firstremoval step for removing low-boiling-point impurities from thehigh-boiling-point waste photoresist stripper, a second removal step forrecovering a stripper solvent composition while removinghigh-boiling-point impurities from the high-boiling-point wastephotoresist stripper without the low-boiling-point impurities, and athird removal step for removing trace water from the stripper solventcomposition without the high-boiling-point impurities, thus obtaining ahigh-purity recycled stripper mixture; and performing additionalstripper recycling so that a high-boiling-point stripper solvent isadditionally recovered from a high-boiling-point residue including thehigh-boiling-point impurities removed by the second removal step of thetotal stripper recycling.

Also, the method of the present invention further includes separatestripper recycling so that the stripper solvent composition recovered bythe second removal step of the total stripper recycling and thehigh-boiling-point stripper solvent additionally recovered through theadditional stripper recycling are separately recovered as individualhigh-purity recycled strippers.

In an exemplary embodiment of the present invention, the pretreatingcomprises neutralization for maintaining pH of the high-boiling-pointwaste stripper to 6.5˜8.5 so as to remove the organic acid component;precipitation for 1˜12 hr so as to remove a neutralized product andfloating and insoluble components generated in a stripping process; andfiltration including primary filtration using a 20˜100 an sieve andsecondary filtration using a 0.1˜10 μm sieve.

In an exemplary embodiment of the present invention, the first removalstep of the total stripper recycling comprises heating thehigh-boiling-point waste photoresist stripper transported to adistillation tower of a first distillation device to a temperature equalto or higher than a boiling point of water so as to enable evaporationof the low-boiling-point impurities; performing first distillation bymaintaining a temperature of a reboiler connected to the distillationtower of the first distillation device to 85° C. or less; and reducingan inner pressure of the distillation tower of the first distillationdevice to prevent promotion of thermal decomposition of thehigh-boiling-point stripper solvent contained in the high-boiling-pointwaste photoresist stripper; and condensing and collecting the extractedlow-boiling-point impurities.

In an exemplary embodiment of the present invention, the second removalstep of the total stripper recycling comprises transporting thehigh-boiling-point waste photoresist stripper without thelow-boiling-point impurities to a distillation tower of a seconddistillation device, and then performing rapid heating to a temperatureequal to or higher than a boiling point of a component having thehighest boiling point among stripper solvent components; performingsecond distillation by maintaining a temperature of a reboiler connectedto the distillation tower of the second distillation device to 160° C.or less; condensing the stripper solvent composition extracted from atop of the distillation tower through second distillation, using acondenser so as to be recovered and simultaneously concentrating, as awaste byproduct, the high-boiling-point impurities other than thestripper solvent composition, in a bottom of the tower and the reboiler,and removing them; and reducing an inner pressure of the distillationtower of the second distillation device to prevent promotion of thermaldecomposition of the high-boiling-point stripper solvent.

In an exemplary embodiment of the present invention, the third removalstep of the total stripper recycling comprises transporting the strippersolvent composition obtained in the second removal step to adistillation tower of a third distillation device, and performing thirddistillation under a condition of a temperature of the reboiler beingset to 120° C. or less; reducing an inner pressure of the distillationtower of the third distillation device to prevent promotion of thermaldecomposition of the high-boiling-point stripper solvent; condensingtrace water and volatiles removed by third distillation, using acondenser, and then re-circulating them to the first distillationdevice; and passing the stripper solvent, which is a high-purityrecycled stripper mixture satisfying high-purity electronic gradequality standard by removal of the trace water, through a 1-micronfilter, and then transporting it to a storage tank.

In an exemplary embodiment of the present invention, the additionalstripper recycling comprises transporting the high-boiling-point residueincluding the high-boiling-point impurities removed by the secondremoval step of the total stripper recycling, to a distillation tower ofa fourth distillation device; reducing an inner pressure of thedistillation tower of the fourth distillation device to preventpromotion of thermal decomposition of the stripper solvent contained inthe high-boiling-point residue; performing fourth distillation bymaintaining a temperature of a reboiler connected to the distillationtower of the fourth distillation device to a temperature of 160° C. orless; refluxing the high-boiling-point stripper solvent condensed by thecondenser after having been volatilized from the waste byproduct in thedistillation tower of the fourth distillation device, to a top of thedistillation tower of the fourth distillation device until it satisfieshigh-purity electronic grade quality standard; and recovering thehigh-boiling-point stripper solvent satisfying the standard, passing itthrough the 1-micron filter, and transporting it to a storage tank.

In particular, the fourth distillation of the additional stripperrecycling may be optimally controlled so as to maximally retarddeposition of the photoresist resin while monitoring an extent ofviscosification of the high-boiling-point stripper solvent contained inthe high-boiling-point residue.

More preferably, when viscosity of the high-boiling-point strippersolvent does not exceed a maximum threshold viscosity, the wastebyproduct is circulated to an upside of the reboiler of the fourthdistillation device so as to make a predetermined flow in the reboiler,thereby maximally retarding a deposition time of the photoresist resin;in contrast, when the viscosity of the high-boiling-point strippersolvent exceeds a maximum threshold viscosity, a flow rate of the wastebyproduct fed to the reboiler is increased, thereby lowering theviscosity of the high-boiling-point stripper solvent.

In an exemplary embodiment of the present invention, the separatestripper recycling comprises transporting the stripper solventcomposition recovered through the second removal step using the seconddistillation device and the high-boiling-point stripper solventrecovered through the additional stripper recycling, to a fifthdistillation device; separately recovering individual high-purityelectronic grade recycled stripper solvents depending on the boilingpoint of each stripper solvent of the stripper solvent composition byincreasing a number of theoretical plates of a distillation tower of thefifth distillation device while a spiral stirring type column device ofthe fifth distillation device is rotated at 2,500 rpm at maximum; andpassing the recovered individual recycled stripper solvents through the1-micron filter, and respectively transporting them to individualstripper solvent storage tanks.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a process of recycling a high-boiling-point wastephotoresist stripper according to the present invention; and

FIG. 2 illustrates a system for implementing the process of recycling ahigh-boiling-point waste photoresist stripper according to the presentinvention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, a detailed description will be given of the presentinvention.

As used herein, the term “low-boiling-point impurities” refers toimpurities having a boiling point lower than the boiling points ofindividual stripper solvents contained in a high-boiling-point wastephotoresist stripper, and typically indicates water such as cleaningwastewater or a small amount of organic solvent such as IPA as a wastesolvent.

Also as used herein, the term “high-boiling-point impurities” refers toimpurities having a boiling point higher than the boiling points ofindividual stripper solvents contained in a high-boiling-point wastephotoresist stripper, and preferably indicates impurities having aboiling point of 235° C. or more, typically for example, a photoresistresin stripped after having been used for forming a resist pattern in agate process of a transistor, including other impurities such as a smallamount of nonionic surfactant, etc.

Also as used herein, the term “high-purity electronic grade strippersolvent” means that a stripper solvent exhibits quality standardequivalent to that of a new solvent used to prepare an undilutedphotoresist stripper, for example, a purity of 99.5% or more, a watercontent of 0.1% or less and a heavy metal or total metal content at thelevel of ppb, wherein the lower limit of the water content is notparticularly set but is typically about 0.001%, and the total metalcontent is preferably 500 ppb or less, and the lower limit thereof isnot particularly limited but approximates to 1 ppb.

Also as used herein, the term “high-boiling-point stripper solvent”refers to a stripper solvent having a boiling point higher by at least10° C. than about 220° C. corresponding to the upper limit of theboiling point of a general stripper solvent contained in ahigh-boiling-point waste photoresist stripper, and is preferably aphotoresist stripper solvent having a boiling point of 235° C. or morefor use in a stripping process. It is typically exemplified by HEPhaving high stripper solubility as an organic amine solvent.

To aid understanding of the present invention, a waste photoresiststripper containing a high-boiling-point stripper solvent, etc. isdescribed below.

The recyclable stripper solvent in the waste photoresist stripper, whichmay be recovered by the recycling method according to the presentinvention, is an organic solvent mixture comprising a protic solvent, anaprotic solvent and a water-soluble organic amine solvent, and theorganic amine solvent is 1-piperazineethanol (hereinafter referred to as“HEP”) which is a typical resource of a high-boiling-point strippersolvent.

HEP which is a typical valuable resource of a high-boiling-pointstripper solvent as the water-soluble organic amine solvent may becontained in an amount of 15˜40 parts by weight based on 100 parts byweight of the high-boiling-point waste photoresist stripper.

HEP which is a high-boiling-point stripper solvent has highhygroscopicity and a water content of 0.1% or less and is thus difficultto purify, and also has high heat sensitivity due to high-boiling-pointproperties and thus causes thermal decomposition and color change.

Such thermal decomposition and color change may occur under conditionsof a temperature of 85° C. or more with a water content of at least 3˜5parts by weight in the waste photoresist stripper, a temperature of 200°C. or more with an HEP content of at most 10˜15 parts by weightregardless of the water content, or a temperature of 160° C. or morewith an HEP content of at least 10˜15 parts by weight.

The organic amine solvent functions to infiltrate the polymericstructure of a photoresist (PR) which is denatured or crosslinked invarious courses of etching, painting, ion implantation, etc. in thestripping process to thus destruct intramolecular or intermolecularattraction, and thereby the photoresist is dissolved and easily removed.

Another high-boiling-point property of HEP which is a high-boiling-pointstripper solvent may be exemplified by viscosification. When thissolvent is in an amount equal to or higher than a predetermined weightratio based on the relative weight ratio with the photoresist resin ofthe waste photoresist stripper, it may trigger solidification of thephotoresist resin and thus may move up the deposition time whilegradually increasing the viscosity thereof. Particularly,viscosification may drastically accelerate in the temperature range of160° C. or more, undesirably incurring processing difficulties whichimpede the process of recycling the high-boiling-point stripper solventfrom the waste stripper. For this reason, a large amount of HEP in thewaste stripper may be removed and discarded as a residue together withthe high-boiling-point impurities.

In the recyclable stripper solvent of the waste photoresist stripper,the protic solvent (a protonic glycol ether compound) includesdiethyleneglycol monomethyl ether (hereinafter referred to as “MDG”),diethyleneglycol monobutyl ether (hereinafter referred to as “BDG”), ordiethyleneglycol monoethyl ether (hereinafter referred to as “EDG”), andMDG, BDG or EDG may be used alone or in combination.

The protic solvent is a compound having high vapor pressure and is lesslost by heating or evaporation. It is responsible for increasingsolubility of the photoresist and dissolving the photoresist stripped byan alkaline compound so that hydroxide ions generated from the alkalinecompound may effectively infiltrate a space between the photoresist andthe glass substrate in a stripping process to thus execute dissolutionand stripping functions. Furthermore, it is maximized in wettabilitybecause of low interfacial tension to thus prevent reattachment of thephotoresist which mainly takes place in a cleaning process, therebymaximizing stripping efficiency.

In the recyclable stripper solvent of the waste photoresist stripper,the aprotic solvent (a non-protonic polar compound) includes dimethylacetamide (hereinafter referred to as “DMAc”), N-methylpyrrolidone(hereinafter referred to as “NMP”) or dimethylsulfoxide (hereinafterreferred to as “DMSO”), and DMAc, NMP or DMSO may be used alone or incombination.

The aprotic solvent has high solubility of a photoresist in thestripping process, and thus functions to dissolve the photoresiststripped by the amine compound, thereby preventing reattachment of thephotoresist which mainly takes place in the cleaning process andmaximizing the cleaning effects.

The system for recycling the high-boiling-point waste photoresiststripper according to an exemplary embodiment of the present inventionis specified below with reference to the appended drawings.

FIG. 1 is a flowchart illustrating the process of highly recovering ahigh-purity electronic grade high-boiling-point stripper solvent from ahigh-boiling-point waste photoresist stripper according to an embodimentof the present invention, and FIG. 2 is a view illustrating the systemfor recycling the high-boiling-point waste photoresist stripperaccording to the present invention.

As illustrated in FIG. 1, the method of recycling the high-boiling-pointwaste photoresist stripper according to the present invention includes apretreatment process, total and additional stripper recycling processesincluding impurity removal steps, and recovery processes of strippersolvent and additional high-boiling-point stripper solvent. Among these,the pretreatment process may be optionally performed or not depending onthe pH of the high-boiling-point waste photoresist stripper includingthe high-boiling-point stripper solvent, and the kinds and amounts ofinsoluble materials or impurities.

Furthermore, the total and additional stripper recycling processesincluding impurity removal steps, and the recovery processes of strippersolvent and additional high-boiling-point stripper solvent are nottemporally spatially separated from each other, but are a series of unitoperations in which recovering the stripper solvent or the additionalhigh-boiling-point stripper solvent is carried out in coincidence withremoving the impurities.

The high-boiling-point waste photoresist stripper is collected, mixed ina separate waste stripper storage tank, fed to a pretreatment unit so asto undergo neutralization, precipitation and filtration. By such apretreatment process, solids, insoluble denatured photoresist andorganic acid components are removed from the high-boiling-point wastestripper.

In the pretreatment process, neutralization is performed to remove adenatured organic acid component which is contained in thehigh-boiling-point waste stripper by being incorporated in an etchingprocess or a developing process during fabrication of a semiconductorwafer or TET-LCD. When the pH of the waste stripper is 4˜6 due to thepresence of the organic acid component, the transport lines of thesubsequent total and additional stripper recycling processes or thedistillation equipment may corrode, thus remarkably lowering recyclingseparation efficiency and instability of the recycling process. Hence,neutralization in the pretreatment process enables the organic acidcomponent to be removed so that the pH of the waste stripper ispreferably maintained in the range of 6.5˜8.5.

In the pretreatment process, subsequent precipitation and filtration areperformed to remove not only the neutralized product but also thefloating and insoluble components (mainly comprising decompositionresidue of the polymer of the photoresist and heavy metal componentsgenerated in the conductive metal film etching process) generated in thestripping process. Precipitation is implemented for a period of timeenough to induce precipitation of the high-boiling-point waste stripperin the storage tank, for example, 1˜12 hr, and preferably 2˜5 hr, andthen filtration is primarily conducted using a 20˜100 an sieve and thensecondarily performed using a 0.1˜10 an sieve, thereby separating theprecipitate and the waste stripper from each other.

Preferably, in the pretreatment process, filtration is primarilyperformed using a 325 mesh (about 44 μm) sieve and then secondarilyconducted using a filter having a pore size of 1 μm.

After the pretreatment process as above, the total stripper recyclingfor removing impurities from the high-boiling-point waste photoresiststripper through three steps is implemented.

The total stripper recycling includes a total of three impurity removalsteps including a first removal step for removing low-boiling-pointimpurities (low-boiling-point waste impurities) such as water, etc. fromthe high-boiling-point waste photoresist stripper, a second removal stepfor removing a high-boiling-point residue (high-boiling-point wasteimpurities) including high-boiling-point impurities such as aphotoresist resin, etc., and a third removal step for continuouslyremoving trace water (residual waste trace water).

The system for recycling the high-boiling-point waste photoresiststripper according to the present invention includes a firstdistillation device for the first removal step (for removing thelow-boiling-point impurities such as water, etc. from thehigh-boiling-point waste photoresist stripper), a second distillationdevice for the second removal step (for removing the high-boiling-pointresidue including high-boiling-point impurities such as a photoresistresin, etc.), and a third distillation device for the third removal step(for continuously removing trace water).

In the system for recycling the high-boiling-point waste photoresiststripper according to the present invention, construction of the firstdistillation device for use in the first removal step of the totalstripper recycling is as follows.

The first distillation device is used to remove low-boiling-pointimpurities such as water, etc. from the high-boiling-point wastephotoresist stripper, and includes a feed tank T-1 for storing thepretreated high-boiling-point waste photoresist stripper, a firsttransport pump F-1 for transporting the high-boiling-point wastestripper from the feed tank T-1 to a distillation tower D-1, and adistillation tower D-1 having 15˜25 and preferably about 20 theoreticalplates for purification.

The distillation tower D-1 of the first distillation device isresponsible for a heating function to a temperature equal to or higherthan the boiling point of water so as to enable evaporation of thelow-boiling-point impurities such as water, etc. contained in thetransported waste stripper, and a reboiler 3 as a heater therefor isseparately connected to the bottom of the distillation tower D-1.

In order to prevent promotion of thermal decomposition when thehigh-boiling-point waste stripper in the distillation tower D-1 isheated, a vacuum pump 21 is connected to the top of a temporary storagetank 2 for temporarily storing the stripper solvent, with a condenser 1and the temporary storage tank 2 being sequentially connected to the topof the distillation tower D-1.

With the goal of preventing promotion of thermal decomposition of thehigh-boiling-point waste stripper, the vacuum pump 21 is actuated tothus reduce the inner pressure of the distillation tower D-1 so thatvacuum operation is carried out. Preferably, the pressure for vacuumdistillation is set to 110 torr or less and the temperature of thereboiler 3 is set to 80° C. or less.

While maintaining such purification conditions, low-boiling-pointimpurities such as water, IPA, etc. are distilled and extracted from thetop of the distillation tower, and the extracted low-boiling-pointimpurities are condensed by the condenser 1 connected to the top of thedistillation tower D-1 and then recovered in the temporary storage tank2, and the recovered low-boiling-point impurities are transported to aseparate collection tank T-2 by the actuation of a second transport pump1-1, and then discarded.

Based on the construction of the first distillation device, removing thelow-boiling-point impurities from the high-boiling-point wastephotoresist stripper is specified below.

During the total stripper recycling, the first removal step for removingthe low-boiling-point impurities from the high-boiling-point wastephotoresist stripper is performed by primarily distilling thehigh-boiling-point waste photoresist stripper under conditions of thetemperature of the reboiler being set to 85° C. or less, thereby easilyremoving the low-boiling-point impurities.

As illustrated in FIG. 2, the high-boiling-point waste photoresiststripper is fed to the feed tank T-1, and then transported to thedistillation tower D-1 of the first distillation device, having 15˜25and preferably about 20 theoretical plates for purification, by theactuation of the first transport pump F-1.

Subsequently, the waste stripper transported to the distillation towerD-1 of the first distillation device is heated to a temperature equal toor higher than the boiling point of water by means of the reboiler 3 soas to enable evaporation of the low-boiling-point impurities such aswater, etc.

The stripper solvent components contained in the waste stripper shouldnot be susceptible to changes in physicochemical properties includingdecomposition or deformation when exposed at high temperature for a longperiod of time. Especially, HEP which is a high-boiling-point strippersolvent may be promoted in thermal decomposition due to thermal damagewhen the temperature is 85° C. or more under conditions of the watercontent in the waste stripper being at least 3˜5 wt % with high heatsensitivity because of the high-boiling-point properties.

To prevent promotion of thermal decomposition, the vacuum pump 21connected to the distillation tower D-1 is actuated to thus reduce theinner pressure of the tower so as to carry out vacuum operation.Preferably, the pressure for vacuum distillation is set to 110 torr orless, and the temperature of the reboiler 3 is set to 80° C. or less.

Under such purification conditions, the low-boiling-point impuritiessuch as water, IPA, etc. are distilled and extracted from the top of thedistillation tower, and the extracted low-boiling-point impurities arecondensed by the condenser 1, recovered in the temporary storage tank 2,transported to the separate collection tank T-2 by the actuation of thesecond transport pump 1-1, and then discarded.

Also in the system for recycling the high-boiling-point wastephotoresist stripper according to the present invention, construction ofthe second distillation device for use in the second removal step of thetotal stripper recycling is as follows.

The second distillation device plays a role in removing thehigh-boiling-point residue including the high-boiling-point impuritiesfrom the waste stripper after the first removal step, and simultaneouslyin recycling the stripper solvent composition.

The second distillation device includes a distillation tower D-2 having7˜15 and preferably about 10 theoretical plates for purification, towhich the waste stripper after the first removal step is discharged fromthe reboiler 3 of the first distillation device by the actuation of athird transport pump 1-2; a reboiler 7 and a vacuum pump 22 connected tothe distillation tower D-2 to prevent changes in physicochemicalproperties, including decomposition or deformation by heat, of thestripper solvent component (especially, HEP which is ahigh-boiling-point stripper solvent sensitive in thermal damage due tohigh-boiling-point properties) contained in the waste stripper in thedistillation tower D-2; a condenser 4 for condensing the total strippersolvent composition extracted from the waste stripper; and a temporarystorage tank 5 for temporarily storing the stripper solvent compositionrecovered after having been condensed by the condenser 4.

The distillation tower D-2 of the second distillation device isresponsible for removing the high-boiling-point residue including thehigh-boiling-point impurities from the waste stripper after the firstremoval step and simultaneously for heating and distilling the wastestripper after the first removal step so as to recycle the strippersolvent composition, and the reboiler 7 as a heater therefor isseparately connected to the bottom of the distillation tower D-2.

The vacuum pump 22 is connected to the top of the temporary storage tank5 for temporarily storing the stripper solvent, with the condenser 4 andthe temporary storage tank 5 being sequentially connected to the top ofthe distillation tower D-2.

Also, connected to the outlet of the temporary storage tank 5 are afifth transport pump 2-1 and a sixth transport pump 2-2, which arereflux pumps for transporting, to a third distillation device, thestripper solvent composition condensed by the condenser 4 of the seconddistillation device and recovered in the temporary storage tank 5.

The high-boiling-point impurities removed from the waste stripper areconcentrated and left behind in the bottom 6 of the tower and thereboiler 7 to the extent of not deposited through solidification.

Based on the construction of the second distillation device, removingthe high-boiling-point impurities from the high-boiling-point wastephotoresist stripper is specified below.

During the total stripper recycling, the second removal step forremoving the high-boiling-point impurities from the high-boiling-pointwaste photoresist stripper without the low-boiling-point impurities isperformed through second distillation under conditions of thetemperature of the reboiler being set to 160° C. or less, therebyremoving the high-boiling-point residue including the high-boiling-pointimpurities and simultaneously recycling the stripper solvent.

When the high-boiling-point waste photoresist stripper without thelow-boiling-point impurities has a water content of 1˜3 wt %, it istransported to the distillation tower D-2 of the second distillationdevice, having 7˜15 and preferably about 10 theoretical plates forpurification, via the reboiler 3 by the actuation of the third transportpump 1-2.

The stripper solvent component contained in the waste stripper in thedistillation tower D-2 of the second distillation device, especially HEPwhich is a high-boiling-point stripper solvent sensitive to thermaldamage due to high-boiling-point properties, has to prevent changes inphysicochemical properties including decomposition or deformation byheat at high temperature.

Because thermal decomposition and color change occur prominently underconditions of a temperature of 200° C. or more when the amount of HEP isequal to or less than 10˜15 wt % regardless of the water content orunder conditions of a temperature of 160° C. or more when the amount ofHEP is equal to or more than 10˜15 wt %, they may be prevented byactuating the vacuum pump 22 connected to the distillation tower to thusreduce the inner pressure of the tower so that vacuum operation iscarried out. Preferably, the pressure for vacuum distillation is set to90 torr or less, and the temperature of the reboiler 7 is set to 160° C.or less.

In order to remove the high-boiling-point impurities from thehigh-boiling-point waste photoresist stripper transported to thedistillation tower D-2 of the second distillation device, rapid heatingis conducted to a temperature equal to or higher than the boiling pointof the component having the highest boiling point among stripper solventcomponents, and thereby the total stripper solvent composition(high-purity recyclable stripper mixture) constituting the stripper isdistilled and extracted at the same time from the top of thedistillation tower, and the extracted total stripper solvent compositionis sent to the condenser 4 so as to be condensed and thus separated.

Simultaneously, the high-boiling-point impurities such as a photoresistresin, etc. which are dissolved in the waste stripper are concentratedand left behind in the bottom 6 of the tower and the reboiler 7 to theextent of not being deposited through solidification.

When HEP which is a high-boiling-point stripper solvent, havingviscosification as another high-boiling-point property, is in an amountequal to or higher than a predetermined weight ratio based on therelative weight ratio with the photoresist resin of the waste stripper,it may trigger solidification of the photoresist resin and thus may moveup the deposition time while gradually increasing the viscosity thereof.

In particular, viscosification may drastically accelerate in thetemperature range of 160° C. or more, and may cause recyclingdifficulties. To prevent this, a large amount of HEP in the wastestripper is not recovered in the condenser 4 by distillation andextraction, but may be left behind as the residue in the bottom 6 of thetower and the reboiler 7 together with the high-boiling-pointimpurities, and then removed and discarded as a waste byproduct.

Hence, in the present invention, the waste byproduct comprising theresidue (including HEP) left behind in the bottom 6 of the tower and thereboiler 7 together with the high-boiling-point impurities is subjectedto additional stripper recycling using a fourth distillation device tothus additionally recover HEP.

The waste byproduct comprising the high-boiling-point impurities and HEPwhich is a high-boiling-point stripper solvent mixed in a considerableamount is transported to a temporary storage tank 13 connected to thefourth distillation device so as for additional stripper recycling, andthe fourth distillation device for additional secondary recycling isdescribed in detail later.

In the system for recycling the high-boiling-point waste photoresiststripper according to the present invention, construction of the thirddistillation device for use in the third removal step of the totalstripper recycling is as follows.

The third distillation device is used to remove trace water which finelyremains due to hygroscopicity of the stripper solvent component from thestripper solvent composition obtained by the second distillation device,and includes a distillation tower D-3 which receives the strippersolvent composition which is discharged by the actuation of the fifthtransport pump 2-1 and the sixth transport pump 2-2 after having beencondensed by the condenser 4 of the second distillation device andrecovered in the temporary storage tank 5.

The distillation tower D-3 of the third distillation device has 25˜35and preferably about 30 theoretical plates for purification.

Furthermore, the third distillation device includes a reboiler 11 and avacuum pump 23 connected to the distillation tower D-3 to preventchanges in physicochemical properties, including decomposition ordeformation by heat, of the stripper solvent component (especially, HEPwhich is a high-boiling-point stripper solvent sensitive to thermaldamage due to high-boiling-point properties) contained in the wastestripper in the distillation tower D-3.

The reboiler 11 is separately connected to the bottom of thedistillation tower D-3 of the third distillation device and thusperforms a heating function so as to remove trace water from thestripper solvent composition obtained by the second distillation device.

The vacuum pump 23 is connected to the top of a temporary storage tank10 for temporarily storing the stripper solvent, with condensers 8, 9and the temporary storage tank 10 being sequentially connected to thetop of the distillation tower D-3, in order to prevent promotion ofthermal decomposition when the stripper solvent composition in thedistillation tower D-3 is heated.

The third distillation device includes the condenser 9 connected to thetop of the distillation tower D-3 so as to condense the removed tracewater and volatiles, the temporary storage tank 10 for temporarilystoring the condensed stripper solvent, and an eighth transport pump 3-2for finally transporting the stripper solvent in the temporary storagetank 10 and the remaining stripper solvent in the bottom of thedistillation tower D-3 and the reboiler 11, to a recycled strippermixture storage tank T-4.

A 1-micron filter 12 for finally filtering the stripper solvent isdisposed in the flow path from the eighth transport pump 3-2 to therecycled stripper mixture storage tank T-4.

Based on the construction of the third distillation device, removingtrace water from the stripper solvent composition without thehigh-boiling-point impurities is described in more detail below.

The third removal step of the total stripper recycling is performed bysubjecting the stripper solvent composition to third distillation underconditions of the temperature of the reboiler being set to 110° C. orless, thereby removing trace water, ultimately obtaining a high-purityrecycled stripper solvent (a high-purity recycled stripper mixture)containing a portion of the recycled high-boiling-point strippersolvent.

The third distillation device is used to remove trace water which finelyremains due to hygroscopicity of the stripper solvent from the strippersolvent composition obtained by the second distillation device, and isoperated in such a way that the stripper solvent composition condensedby the condenser 4 and recovered in the temporary storage tank 5 istransported to the distillation tower D-3 of the third distillationdevice, having 25˜35 and preferably about 30 theoretical plates forpurification, by the actuation of the fifth transport pump 2-1 and thesixth transport pump 2-2 which are reflux pumps.

Subsequently, the third distillation device performs a process offinally recycling a high-purity electronic grade recycled strippersolvent containing a portion of the recycled high-boiling-point strippersolvent having a water content of 0.1 wt % or less by removing theresidual trace water from the stripper solvent composition recovered bythe second distillation device.

The stripper solvent component contained in the waste stripper in thethird distillation device, especially HEP which is a high-boiling-pointstripper solvent sensitive to thermal damage due to high-boiling-pointproperties, has to prevent changes in physicochemical propertiesincluding decomposition or deformation by heat at high to temperature.

Thermal decomposition and color change may become prominent underconditions of a temperature of 200° C. or more when the amount of HEP isequal to or less than 10˜15 wt % regardless of the water content, andsuch thermal damage may be triggered gradually from 120° C. To preventthis, the vacuum pump 23 connected to the distillation tower is actuatedto thus reduce the inner pressure of the tower so that vacuum operationis carried out. Preferably, the pressure for vacuum distillation is setto 110 torr or less, and the temperature of the reboiler 11 is set to110° C. or less.

Subsequently, in order to remove trace water, which was maximallyremoved by the first distillation device but left behind to the level of1˜3 wt %, from the stripper solvent composition transported to thedistillation tower D-3 of the third distillation device, the residualwater absorbed to the stripper solvent composition is removed throughthe distillation tower having about 30 theoretical plates with highseparation efficiency, after which the water content is maintained at0.1% or less, and generally in the range of 0.001˜0.1%.

The removed trace water and volatiles are condensed by the condenser 9and then re-circulated back to the first distillation device to thus bedistilled, and thereby the water is transported to the separatecollection tank T-2 and then discarded, and part of the stripper solventcontained in the volatiles is sent again to the second distillationdevice and thus recovered without loss.

Part of the stripper solvent, which is recovered in the temporarystorage tank 10 after having been volatilized from the top of the towerand then condensed by the condenser 8, is refluxed to the top of thetower until it satisfies high-purity electronic grade quality standard(purity: 99.5% or more, water content: 0.1% or less, total metalcontent: 100 ppb or less) by the actuation of a seventh transport pump3-1.

Thereafter, the stripper solvent satisfying the above standard isrecovered together with the stripper solvent left behind in the bottomof the tower and the reboiler 11, by the actuation of the eighthtransport pump 3-2, and then passes through the 1-micron filter 12positioned in the recovery path, thereby obtaining a recycled strippersolvent composition satisfying the high-purity electronic grade qualitystandard, which is then immediately transported to the recycled strippermixture storage tank T-4 and stored therein.

When the total stripper recycling including the three impurity removalsteps is carried out in this way, the stripper solvent composition(high-purity recycled stripper mixture) in the high-boiling-point wastephotoresist stripper may be recovered at high purity at the same time.

Below is a description of additional stripper recycling for additionallyrecovering the high-boiling-point stripper solvent from thehigh-boiling-point residue of the high-boiling-point waste photoresiststripper removed by the second removal step of the total stripperrecycling.

The system for recycling the high-boiling-point waste photoresiststripper according to the present invention includes a fourthdistillation device for further obtaining a stripper solvent (HEP) byadditionally recycling the waste byproduct comprising thehigh-boiling-point impurities and the high-boiling-point residue(including HEP) left behind in the bottom 6 of the tower of the seconddistillation device and the reboiler 7.

A temporary storage tank 13 for temporarily storing the waste byproductand a ninth transport pump 4-5 for sending the waste byproduct to thedistillation tower D-4 are disposed between the reboiler 7 separatelyconnected to the bottom 6 of the tower of the second distillation deviceand the distillation tower D-4 of the fourth distillation device.

The distillation tower D-4 of the fourth distillation device has 8˜12and preferably about 10 theoretical plates for purification.

The fourth distillation device includes a vacuum pump 25 for reducingthe inner pressure of the tower and a reboiler 16 for heating anddistilling the waste byproduct, which are respectively connected to thetop and the bottom of the distillation tower D-4, in order to enable thewaste byproduct transported to the distillation tower D-4, especiallythe high-boiling-point stripper solvent sensitive to thermal damage dueto its high-boiling-point properties to prevent changes inphysicochemical properties including decomposition or deformation byheat.

Also, the fourth distillation device includes a condenser 14 forcondensing the stripper solvent volatilized from the waste byproduct inthe distillation tower D-4, and a temporary storage tank 15 forrecovering and temporarily storing the condensed stripper solvent.

Also, the fourth distillation device further includes control membersfor monitoring the extent of viscosification of the high-boiling-pointstripper solvent contained in the high-boiling-point residue andmaximally increasing the recycling yield of HEP while maximallyretarding the deposition of the photoresist resin, when the photoresistresin which is not sufficiently concentrated, of the waste byproduct inthe reboiler 16, is transported to the impurity collection tank T-3 anddiscarded.

Specifically, in the fourth distillation device, a viscometer 18 formeasuring the viscosity of the residue and a flow rate meter forcontrolling the flow rate in the reboiler 16 are disposed in theconnection line between the reboiler 16 and the collection tank T-3, andare controlled by a controller 18 a.

More specifically, of the flow rate meter, a first flow rate controlvalve 19 is disposed together with a tenth transport pump 4-4 in thecirculation line upwards from the outlet of the reboiler 16, and asecond flow rate control valve 20 is disposed together with an eleventhtransport pump 4-3 in the connection line between the outlet of thereboiler 16 and the collection tank T-3.

The fourth distillation device includes a twelfth transport pump 4-1 anda thirteenth transport pump 4-2 connected to the outlet of the temporarystorage tank 15 so as to transport the finally recovered strippersolvent satisfying the above standard, that is, HEP, to the recycledstripper mixture storage tank T-4, and a 1-micron filter 12 for finallyfiltering the transported stripper solvent.

Based on the construction of the fourth distillation device, additionalstripping recycling for additionally recovering the high-boiling-pointstripper solvent from the high-boiling-point residue of thehigh-boiling-point waste stripper is described below.

The additional stripper recycling includes supplying thehigh-boiling-point waste residue including the high-boiling-pointimpurities removed by the second distillation device, to the fourthdistillation device, and removing the high-boiling-point impurities(high-boiling-point waste impurities) from the high-boiling-point wasteresidue including the high-boiling-point impurities through the fourthremoval step using the fourth distillation device and simultaneouslyextracting and recovering the high-purity electronic gradehigh-boiling-point stripper solvent due to the removal of thehigh-boiling-point impurities.

Preferably, the additional stripper recycling is carried out throughfourth distillation under conditions in which the high-boiling-pointresidue including the high-boiling-point impurities removed by seconddistillation of the total stripper recycling is maintained at 160° C. orless in the reboiler and under conditions of optimally controlling theextent of viscosification of the high-boiling-point stripper solventcontained in the high-boiling-point residue so as to maximally retardthe deposition of the photoresist resin. Thereby, only the high-purityhigh-boiling-point stripper solvent may be additionally recycled incoincidence with removing the high-boiling-point impurities.

The waste byproduct comprising the high-boiling-point impurities and HEPwhich is a high-boiling-point stripper solvent mixed in a considerableamount is transported to the temporary storage tank 13 connected to thefourth distillation device for additional stripper recycling.

As illustrated in FIG. 2, the high-boiling-point waste photoresiststripper from which the low-boiling-point impurities were primarilyremoved is sent to the second distillation device D-2, after which it isextracted in the form of the stripper solvent composition andsimultaneously part of the high-boiling-point stripper solvent which wasnot recovered by extraction is left behind as the waste byproduct in thebottom 6 of the tower and the reboiler 7 together with thehigh-boiling-point impurities. The waste byproduct is sent to thetemporary storage tank 13 connected with the fourth distillation devicefor additional stripper recycling.

Subsequently, the ninth transport pump 4-5 is actuated so that the wastebyproduct is transported to the distillation tower D-4 of the fourthdistillation device having 8˜12 and preferably about 10 theoreticalplates for purification.

The waste byproduct transported to the distillation tower D-4 of thefourth distillation device contains HEP which is a high-boiling-pointstripper solvent sensitive to thermal damage due to high-boiling-pointproperties. Because such a high-boiling-point stripper solvent suffersfrom changes in physicochemical properties including decomposition ordeformation by heat at high temperature, such changes have to beprevented.

Also, thermal decomposition and color changes may occur prominentlyunder conditions of a temperature of 160° C. or more when the amount ofHEP is equal to or more than 10˜15 wt % regardless of the water content,and thus have to be prevented.

Hence, the vacuum pump 25 connected to the distillation tower D-4 of thefourth distillation device is actuated to thus reduce the inner pressureof the tower, and thereby vacuum operation is carried out. Preferably,the pressure for vacuum distillation is set to 80 torr or less, and thetemperature of the reboiler 16 is set to 160° C. or less.

When HEP which is a high-boiling-point stripper solvent, havingviscosification as the high-boiling-point property, is in an amountequal to or higher than a predetermined weight ratio based on therelative weight ratio with the photoresist resin in the waste stripper,it may trigger solidification of the photoresist resin and may move upthe deposition time while gradually increasing the viscosity thereof.

Particularly, viscosification may drastically accelerate in thetemperature range of 160° C. or more. In the case where the wastebyproduct is purified through a conventional recycling method, thephotoresist resin is deposited and solidified in the bottom 17 of thetower and the reboiler 16, thereby breaking the gas-liquid equilibriumof the distillation line based on the material resin, decreasing therecycling efficiency and lowering the distillation recovery efficiency,resulting in inefficient distillation operation.

Also, when the photoresist resin, which is not sufficientlyconcentrated, of the waste byproduct in the reboiler 16, is transportedto the impurity collection tank T-3 and discarded, HEP which is ahigh-boiling-point stripper solvent contained in a large amount in thewaste stripper is transported and discarded together, making itdifficult to achieve high recycling yield due to an increase in loss ofthe HEP solvent which is an expensive valuable resource.

Therefore, in the present invention, optimal control is implemented tomonitor the extent of viscosification of the high-boiling-point strippersolvent contained in the high-boiling-point residue, and to maximallyincrease the recycling yield of HEP while maximally retarding thedeposition of the photoresist resin.

Specifically, the fourth distillation device includes a viscometer 18for measuring the viscosity of the residue, a flow rate meter forcontrolling the flow rate in the reboiler 16, and a controller forintegrated control thereof.

Referring to FIG. 2, distillation is carried out in the distillationtower D-4 of the fourth distillation device, and thereby the strippersolvent composition including HEP in the form of a mixture from thewaste byproduct is recovered in the temporary storage tank 15 throughthe condenser 14. While the concentration of HEP of the waste byproductsupplied to the reboiler 16 connected to the distillation tower D-4gradually increases during the recovery process, the relative weightratio with the photoresist resin also increases, and thus the viscosityof the HEP solvent is simultaneously increased.

When the viscosity of the HEP solvent is increased, a portion of thewaste byproduct including HEP is fed to the viscometer 18 and thuschanges in the viscosity of the waste byproduct are measured, so thatthe deposition time through solidification of the photoresist resintherein may be indirectly measured.

In order to indirectly measure the deposition time throughsolidification of the photoresist resin using the viscometer 18, acorrelation between the deposition time through solidification of thephotoresist resin and changes in the viscosity of HEP over time byviscosification depending on changes in the weight ratio of HEP in thewaste byproduct is made in advance and utilized.

As the concentration of HEP of the waste byproduct in the reboiler 16increases, viscosification is considerably progressed due to an increasein the relative weight ratio with the photoresist resin, and thus thephotoresist resin begins to be deposited as a solid component while theviscosity of HEP is increased.

The viscosity of HEP measured by the viscometer 18 may be determined tobe maximum threshold viscosity at a point of time at which thephotoresist resin is deposited as a solid component, and the level ofthe waste byproduct in the reboiler 16 at the same point of time may bedecided as the minimum level which enables additional recycling of HEP.

Thus, in the case where the viscosity of HEP measured by the viscometer18 does not exceed the maximum threshold viscosity, the first flow ratecontrol valve 19 is opened and the tenth transport pump 4-4 is actuatedin response to an output signal by the controller 18 a, so that thewaste byproduct is circulated to the upside of the reboiler 16, therebymaking a predetermined flow in the reboiler 16. Accordingly, the pointof time at which the photoresist resin is deposited may be maximallyretarded tanks to an effect of mitigation of the viscosification.

In contrast, in the case where the viscosity of HEP measured by theviscometer 18 reaches the maximum threshold viscosity, the flow rate ofthe waste byproduct fed to the reboiler 16 is increased so as todecrease the viscosity of HEP which is maximally viscosified.

The second flow rate control valve 20 is opened and the eleventhtransport pump 4-3 is actuated in response to an output signal by thecontroller 18 a, whereby a portion of the waste byproduct in which HEPthat is a high-boiling-point stripper solvent is maximally viscosifiedis transported to the separate collection tank T-3.

Simultaneously, the ninth transport pump 4-5 is actuated in response toanother output signal by the controller 18 a, so that the flow rate ofthe waste byproduct fed to the reboiler 16 is increased, and thereby thelevel of the waste byproduct in the reboiler 16 may be kept to equal toor higher than the minimum level which enables additional recycling ofHEP.

The recycled HEP solvent, which is the high-boiling-point strippersolvent including part of the stripper solvent composition that isrecovered in the temporary storage tank 15 after having been volatilizedfrom the waste byproduct in the distillation tower D-4 and thencondensed by the condenser 14, is refluxed to the top of thedistillation tower D-4 until it satisfies the high-purity electronicgrade quality standard (purity: 99.5% or more, water content: 0.1% orless, total metal content: 100 ppb or less) by the actuation of thetwelfth transport pump 4-1.

Then, the HEP solvent satisfying the above standard is recovered by theactuation of the twelfth transport pump 4-1 and the thirteenth transportpump 4-2, and then passes through the 1-micron filter 12, and thusfinally recovered as the recycled high-boiling-point stripper solvent(high-purity recycled high-boiling-point stripper) satisfying thehigh-purity electronic grade quality standard. The finally recoveredrecycled high-boiling-point stripper solvent is immediately transportedto the recycled stripper mixture storage tank T-4 and stored therein.

In coincidence with removing the high-boiling-point impurities from thehigh-boiling-point waste residue including the high-boiling-pointimpurities, HEP which is a high-purity electronic gradehigh-boiling-point stripper solvent may be additionally easily recycled.

Consequently, the total stripper recycling and the additional stripperrecycling may increase the recycling yield of the high-boiling-pointstripper solvent, and enable economical and efficient recycling andrecovery of the high-boiling-point stripper solvent which is ahigh-quality high-purity electronic grade expensive valuable resourcealleviated in problems of thermal decomposition and color change.

Meanwhile, separate stripper recycling may be further performed so as toseparately recover, as individual high-purity recycled strippers, thetotal stripper solvent composition (high-purity recycled strippermixture) from which the high-boiling-point residue including thehigh-boiling-point impurities was removed through the second removalstep using the second distillation device during the total stripperrecycling, and the high-boiling-point stripper solvent (high-purityrecycled high-boiling-point stripper) recovered through the additionalstripper recycling using the fourth distillation device.

Construction of a fifth distillation device for the separate stripperrecycling is as follows.

Separate stripper recycling may be optionally or additionallyimplemented, and enables the stripper solvent composition or the organicsolvent mixture such as the high-boiling-point stripper solvent to beseparately recovered as individual stripper solvents using the fifthdistillation device.

Therefore, adopted as the distillation tower D-5 of the fifthdistillation device is a spiral spinning band type distillation towerwhich includes a spiral stirring type column device made of metal orTeflon therein. As the number of theoretical plates of the towerincreases while the spiral stirring type column device is rapidlyrotated at 2,500 rpm at maximum, high separation efficiency may result,and a mixture without fine impurities or having a narrowed boiling pointwidth may be individually separated at high purity.

The fifth distillation device includes a 1-micron filter 12 for finallyfiltering the individual recovered recycled stripper solvents, andindividual stripper solvent storage tanks T-5, T-6, T-7, T-8 for storingthe filtered stripper solvents.

In order to separately recover, as the individual stripper solvents, thestripper solvent composition or the organic solvent mixture such as thehigh-boiling-point stripper solvent based on the above construction, thestripper solvent composition recovered through the second removal stepusing the second distillation device is transported to the distillationtower D-5 of the fifth distillation device by the actuation of the fifthtransport pump 2-1 and the sixth transport pump 2-2 which are refluxpumps.

The distillation tower D-5 of the fifth distillation device is a spiralspinning band type distillation tower as mentioned above. By increasingthe number of theoretical plates of the tower while the spiral stirringtype column device is rapidly rotated at 2,500 rpm at maximum, thistower exhibits high separation efficiency, and enables individualhigh-purity separation of a mixture without fine impurities or having anarrowed boiling point width.

Specifically, the individual high-purity electronic grade recycledstripper solvents may be sequentially separately recovered depending onthe boiling point of each stripper solvent of the stripper solventcomposition while trace water left behind in an amount of about 1˜3 wt %by being maximally removed from the stripper solvent composition usingthe first distillation device is additionally removed so as to be in thelevel of 0.1% or less.

Finally, the individual recovered recycled stripper solvents passthrough the 1-micron filter 12 and then are respectively transported tothe stripper solvent storage tanks T-5, T-6, T-7, T-8 and storedtherein.

The high-boiling-point stripper solvent recovered through the additionalstripper recycling, especially the high-boiling-point stripper solvent(e.g. HEP solvent) recovered using the fourth distillation device, istransported to the distillation tower D-5 of the fifth distillationdevice by the actuation of the twelfth transport pump 4-1 and thethirteenth transport pump 4-2 which are reflux pumps.

Subsequently, as in the principle in which individual recycled strippersolvents are separately recovered from the stripper solvent composition,individual high-purity electronic grade recycled stripper solvents areseparately recovered from the high-boiling-point stripper solventdepending on the boiling point, pass through the 1-micron filter 12, andthen are transported to the stripper solvent storage tanks T-5, T-6,T-7, T-8 and stored therein.

The high-purity electronic grade stripper solvents and thehigh-boiling-point stripper solvents, which are recovered through theseries of total stripper recycling, additional stripper recycling andseparate stripper recycling as above, may be easily reused uponpreparation of the stripper solvent composition in all of the strippingprocesses in a plurality of manufacturers for fabricating semiconductorwafers or TET-LCD from which waste strippers are discharged.

Below is a description of the example and test examples of the presentinvention and comparative examples.

EXAMPLE

The high-boiling-point waste photoresist stripper generated in TET-LCDand semiconductor manufacturing processes was subjected to totalstripper recycling using first to third distillation devices, additionalstripper recycling using a fourth distillation device, and separatestripper recycling using a fifth distillation device according to thepresent invention. The composition of the waste stripper used herein isshown in Table 1 below.

TABLE 1 Stripper Solvent Components (wt %) Impurity Components (wt %)DMAc MDG NMP HEP Photoresist resin Water IPA Others High-boiling-point14 17 10 31 4.5 17 5 1.5 waste stripper

Test Example 1

Removing the low-boiling-point impurities from the high-boiling-pointwaste photoresist stripper including components shown in Table 1,namely, removing the low-boiling-point impurities using a firstdistillation device (first removal step) in total stripper recyclingamong stripper recycling processes according to the present inventionwas performed, after which the amounts of removed water and IPA (IsoPropyl Alcohol) corresponding to the low-boiling-point impurities weremeasured. The results are shown in Table 2 below.

TABLE 2 1^(st) Removal Step After 1^(st) Removal Step Vacuum Pressure(torr) 110 — Reflux Ratio 5 — Reboiler Temp. (° C.) 75 — Actual Numberof Tower Plates 20 — Residual IPA content (%) — 0.05 Residual Watercontent (%) — 1.9

As is apparent from Table 2, after the first removal step of the totalstripper recycling, the low-boiling-point impurities such as water, IPA,etc. were extracted and removed from the high-boiling-point wastephotoresist stripper.

Test Example 2

After removal of the low-boiling-point impurities (first removal step)in the total stripper recycling, the second removal step for removingthe high-boiling-point waste residue from the high-boiling-point wastestripper was performed using a second distillation device, and then therecycling yield of HEP which is a high-boiling-point stripper solventwas measured. The results are shown in Table 3 below.

TABLE 3 Total Stripper After Total Recycling Stripper Recycling VacuumPressure (torr) 90 — Reflux Ratio 3 — Reboiler Temp. (° C.) 146 — ActualNumber of Tower Plates 10 — 1^(st) HEP Yield (%, wt) — 15

As is apparent from Table 3, the high-boiling-point waste residue(high-boiling-point waste impurities) was removed through the secondremoval step of the total stripper recycling, after which a strippersolvent composition was obtained, and the HEP yield of the compositionwas 15 wt % or more.

Test Example 3

After removal of the high-boiling-point waste residue (second removalstep) of the total stripper recycling, the third removal step forremoving trace water from the high-boiling-point waste stripper (thestripper solvent composition) was performed using a third distillationdevice, after which the residual water content was measured. The resultsare shown in Table 4 below.

TABLE 4 2^(nd) Removal Step After 2^(nd) Removal Step Vacuum Pressure(torr) 110 — Reflux Ratio 3 — Reboiler Temp. (° C.) 109 — Actual Numberof Tower Plates 30 — Residual Water content (%) — 0.07

As is apparent from Table 4, the residual water was removed from thestripper solvent composition, and thus the water content was 0.07%,which is lower than 0.1%.

Test Example 4

The high-boiling-point waste residue removed from the high-boiling-pointwaste stripper was subjected to additional stripper recycling using afourth distillation device, after which the additional recycling yieldof HEP which is a high-boiling-point stripper solvent was measured. Theresults are shown in Table 5 below.

TABLE 5 Additional After Additional Stripper Recycling StripperRecycling Vacuum Pressure (torr) 50 — Reflux Ratio 2 — Reboiler Temp. (°C.) 153 — Actual Number of Tower plates 10 — 2^(nd) HEP Yield (%, wt) —27

As is apparent from Table 5, the additional recovery efficiency of HEPamounted to 27%, which is evaluated to be almost as twice as 15% whichis the first HEP yield. Thus, HEP could be additionally recycled andrecovered.

Test Example 5

In order to separate, as individual stripper solvents, the high-purityelectronic grade stripper solvent mixture including the recovered HEPwhich is a high-boiling-point stripper solvent, separate stripperrecycling using a fifth distillation device was performed, after whichthe amounts of finally recovered high-purity electronic grade recycledsolvents including HEP were analyzed. The results are shown in Table 6below.

TABLE 6 Recycled purity Water IPA content Total Metal (%) content (%)(%) content (ppb) SPCE. ≧99.5 ≦0.1 ≦0.1 ≦100 Storage Tank RecycledStripper ≧99.5 ≦0.07 ≦0.05 ≦100 T-4 Solvent Mixture Storage IndividualT5 DMAc ≧99.5 ≦0.07 ≦0.05 ≦100 Tanks T-5~8 Recycled T6 MDG Stripper T7NMP Solvents T8 HEP

As is apparent from Table 6, the recycled stripper solvent mixture couldbe easily separately recovered as individual high-purity electronicgrade recycled stripper solvents (DMAc, MDG, NMP, and HEP).

According to the present invention, the high-boiling-point recycledstripper (the stripper solvent composition) may be recovered throughtotal stripper recycling using the first to third distillation devices,and furthermore, the high-boiling-point stripper solvent discarded as adistillation residue together with high-boiling-point impurities may beadditionally recovered through additional stripper recycling using afourth distillation device, thus remarkably increasing the recyclingyield of the expensive high-boiling-point stripper solvent and achievingenvironmental improvement effects as well as cost savings due torecycling of valuable resources.

As described hereinbefore, the present invention provides a system andmethod for recycling a high-boiling-point waste photoresist stripper.According to the present invention, in order to increase low recyclingyield of a high-boiling-point stripper solvent which is a problem of aconventional recycling method, a high-quality recycledhigh-boiling-point stripper solvent can be recovered from ahigh-boiling-point waste photoresist stripper or a residue such ashigh-boiling-point impurities. Also, generation of high-boiling-pointproperties such as viscosification, thermal decomposition, etc. in arecycling process, and loss of recycled high-boiling-point strippersolvent can be minimized, thus easily increasing the recycling yield ofthe high-boiling-point stripper solvent.

Through total stripper recycling, a high-boiling-point recycled stripper(a stripper solvent composition) can be recovered, and throughadditional stripper recycling, a high-boiling-point stripper solventdiscarded as a distillation residue together with the high-boiling-pointimpurities can be further recovered, thereby considerably increasing therecycling yield of the expensive high-boiling-point stripper solvent,ultimately achieving cost savings through reuse of valuable resources,and environmental improvement effects.

Also, separate stripper recycling can be optionally performed, so thatthe recovered high-boiling-point stripper solvent composition (mixture)can be separately recovered as individual stripper solvents.

Advanced recycling techniques able to recover expensivehigh-boiling-point stripper organic solvents through recycling andpurification can be ensured, and the high-boiling-point stripper solventwhich is an expensive valuable resource imported completely from abroadcan be recovered in a large amount at high recovery efficiency and thenreused, thereby achieving efficient energy management and enhancingIT-related company competitiveness.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A system for recycling a high-boiling-point waste photoresiststripper, comprising: a first distillation device, a second distillationdevice and a third distillation device, which are disposed in a line toperform total stripper recycling of a pretreated high-boiling-pointwaste photoresist stripper, the first distillation device for removinglow-boiling-point impurities from the high-boiling-point wastephotoresist stripper, the second distillation device for removinghigh-boiling-point impurities from the high-boiling-point wastephotoresist stripper without the low-boiling-point impurities andsimultaneously recovering a stripper solvent composition, and the thirddistillation device for removing trace water from the stripper solventcomposition without the high-boiling-point impurities; and a fourthdistillation device connected to an outlet of the second distillationdevice and disposed adjacent thereto to perform additional stripperrecycling for additionally recovering a high-boiling-point strippersolvent from a high-boiling-point residue including thehigh-boiling-point impurities discharged after having been removed bythe second distillation device, wherein a fifth distillation device isfurther disposed, which is connected to outlets of the seconddistillation device and the fourth distillation device to performseparate stripper recycling for separately recovering, as individualhigh-purity recycled strippers, the stripper solvent compositionrecovered by the second distillation device and the high-boiling-pointstripper solvent additionally recovered by the fourth distillationdevice.
 2. The system of claim 1, wherein the first distillation devicecomprises: a distillation tower, which has 15˜25 theoretical plates forpurification and receives the pretreated high-boiling-point wastephotoresist stripper; a reboiler connected to a bottom of thedistillation tower and set to a temperature of 80° C. or less so as toheat the waste stripper transported to the distillation tower toevaporate the low-boiling-point impurities; a condenser connected to atop of the distillation tower so as to condense the extractedlow-boiling-point impurities; a temporary storage tank connected to thecondenser so that the low-boiling-point impurities condensed by thecondenser are temporarily stored; a second transport pump and a separatecollection tank connected side by side to an outlet of the temporarystorage tank to discharge the low-boiling-point impurities recovered inthe temporary storage tank; and a third transport pump connected to anoutlet of the reboiler to transport the waste stripper without thelow-boiling-point impurities to the second distillation device.
 3. Thesystem of claim 2, wherein a vacuum pump is connected to a top of thetemporary storage tank to reduce an inner pressure of the distillationtower so that vacuum operation is carried out, in order to preventpromotion of thermal decomposition when the high-boiling-point wastestripper in the distillation tower is heated.
 4. The system of claim 1,wherein the second distillation device comprises: a distillation tower,which has 7˜15 theoretical plates for purification and receives thewaste stripper transported from the reboiler of the first distillationdevice; a reboiler connected to a bottom of the distillation tower andset to a temperature of 160° C. or less so as to heat the waste strippertransported to the distillation tower to evaporate the stripper solventcomposition; a condenser connected to a top of the distillation tower soas to condense the extracted stripper solvent composition; a temporarystorage tank for temporarily storing the stripper solvent compositionrecovered after having been condensed by the condenser; and a fifthtransport pump and a sixth transport pump connected side by side to anoutlet of the temporary storage tank so that the stripper solventcomposition recovered in the temporary storage tank is transported tothe third distillation device.
 5. The system of claim 4, wherein avacuum pump is connected to a top of the temporary storage tank toreduce an inner pressure of the distillation tower so that vacuumoperation is carried out, in order to prevent promotion of thermaldecomposition when a stripper solvent component contained in the wastestripper in the distillation tower is heated.
 6. The system of claim 1,wherein the third distillation device comprises: a distillation tower,which has 25˜35 theoretical plates for purification and receives thestripper solvent composition obtained by the second distillation device;a reboiler separately connected to a bottom of the distillation towerand set to a temperature of 110° C. or less to remove trace water fromthe stripper solvent composition transported to the distillation tower;a condenser connected to a top of the distillation tower so that theremoved trace water and volatiles are condensed to be re-circulated tothe first distillation device; an additional condenser connected to thetop of the distillation tower so as to condense a part of the strippersolvent which is volatilized from the top of the tower; a temporarystorage tank for temporarily storing the part of the stripper solventcondensed by the additional condenser; and an eighth transport pump forfinally transporting the stripper solvent in the temporary storage tankand the remaining stripper solvent in the bottom of the distillationtower and the reboiler, to a recycled stripper mixture storage tank. 7.The system of claim 6, wherein a vacuum pump is connected to a top ofthe temporary storage tank to reduce an inner pressure of thedistillation tower so that vacuum operation is carried out, in order toprevent promotion of thermal decomposition when a stripper solventcomponent contained in the waste stripper in the distillation tower isheated.
 8. The system of claim 1, wherein the fourth distillation devicefor additional stripper recycling comprises: a temporary storage tankfor temporarily storing a waste byproduct which is a high-boiling-pointresidue left behind in the bottom of the tower of the seconddistillation device and the reboiler; a distillation tower, which has8˜12 theoretical plates for purification and receives the wastebyproduct in the temporary storage tank by actuation of a ninthtransport pump; a reboiler separately connected to a bottom of thedistillation tower and set to a temperature of 160° C. or less so as toheat the waste byproduct transported to the distillation tower toevaporate the stripper solvent composition; a condenser connected to atop of the distillation tower so as to condense the stripper solventvolatilized from the waste byproduct; a temporary storage tank forrecovering and temporarily storing the condensed stripper solvent; and atwelfth transport pump and a thirteenth transport pump connected to anoutlet of the temporary storage tank so as to transport the recoveredstripper solvent to the recycled stripper mixture storage tank.
 9. Thesystem of claim 8, wherein a vacuum pump is connected to a top of thetemporary storage tank to reduce an inner pressure of the distillationtower so that vacuum operation is carried out, in order to preventpromotion of thermal decomposition when a high-boiling-point strippersolvent component of the waste byproduct in the distillation tower isheated.
 10. The system of claim 8, wherein the fourth distillationdevice further comprises, as control members for maximally increasing arecycling yield of the stripper solvent composition while maximallyretarding deposition of a photoresist resin: a viscometer for monitoringan extent of viscosification of the high-boiling-point stripper solventcontained in the high-boiling-point residue when the photoresist resin,which is not sufficiently concentrated, of the waste byproduct in thereboiler is transported to an impurity collection tank and discarded; afirst flow rate control valve disposed together with a tenth transportpump in a circulation line upwards from an outlet of the reboiler; asecond flow rate control valve disposed together with an eleventhtransport pump in a connection line between the outlet of the reboilerand the collection tank; and a controller for controllingopening/closing of the first and second flow rate control valvesdepending on measurement results of the viscometer.
 11. The system ofclaim 1, wherein the fifth distillation device for separate stripperrecycling comprises: a spiral spinning band type distillation towerincluding therein a spiral stirring type column device made of metal orTeflon so that the stripper solvent composition recovered through thesecond removal step using the second distillation device, and thehigh-boiling-point stripper solvent recovered using the fourthdistillation device are recovered as individual high-purity electronicgrade recycled stripper solvents depending on a boiling point.
 12. Thesystem of claim 6, wherein a 1-micron filter is disposed in a connectionline between the outlet of the temporary storage tank of the thirddistillation device and the recycled stripper mixture storage tank, andin a connection line between an outlet of the fifth distillation deviceand individual stripper solvent storage tanks.
 13. A method of recyclinga high-boiling-point waste photoresist stripper, comprising: pretreatingthe high-boiling-point waste photoresist stripper to remove a solid, aninsoluble denatured photoresist component and an organic acid componenttherefrom; subjecting the pretreated high-boiling-point wastephotoresist stripper to total stripper recycling including a firstremoval step for removing low-boiling-point impurities from thehigh-boiling-point waste photoresist stripper, a second removal step forrecovering a stripper solvent composition while removinghigh-boiling-point impurities from the high-boiling-point wastephotoresist stripper without the low-boiling-point impurities, and athird removal step for removing trace water from the stripper solventcomposition without the high-boiling-point impurities, thus obtaining ahigh-purity recycled stripper mixture; and performing additionalstripper recycling so that a high-boiling-point stripper solvent isadditionally recovered from a high-boiling-point residue including thehigh-boiling-point impurities removed by the second removal step of thetotal stripper recycling, wherein separate stripper recycling is furtherperformed so that the stripper solvent composition recovered by thesecond removal step of the total stripper recycling and thehigh-boiling-point stripper solvent additionally recovered through theadditional stripper recycling are separately recovered as individualhigh-purity recycled strippers.
 14. The method of claim 13, wherein thepretreating comprises neutralization for maintaining pH of thehigh-boiling-point waste stripper to 6.5˜8.5 so as to remove the organicacid component; precipitation for 1˜12 hr so as to remove a neutralizedproduct and floating and insoluble components generated in a strippingprocess; and filtration including primary filtration using a 20˜100 μmsieve and secondary filtration using a 0.1˜10 μm sieve.
 15. The methodof claim 13, wherein the first removal step of the total stripperrecycling comprises: heating the high-boiling-point waste photoresiststripper transported to a distillation tower of a first distillationdevice to a temperature equal to or higher than a boiling point of waterso as to enable evaporation of the low-boiling-point impurities;performing first distillation by maintaining a temperature of a reboilerconnected to the distillation tower of the first distillation device to85° C. or less; and reducing an inner pressure of the distillation towerof the first distillation device to prevent promotion of thermaldecomposition of the high-boiling-point stripper solvent contained inthe high-boiling-point waste photoresist stripper; and condensing andcollecting the extracted low-boiling-point impurities.
 16. The method ofclaim 13, wherein the second removal step of the total stripperrecycling comprises: transporting the high-boiling-point wastephotoresist stripper without the low-boiling-point impurities to adistillation tower of a second distillation device, and then performingrapid heating to a temperature equal to or higher than a boiling pointof a component having the highest boiling point among stripper solventcomponents; performing second distillation by maintaining a temperatureof a reboiler connected to the distillation tower of the seconddistillation device to 160° C. or less; condensing the stripper solventcomposition extracted from a top of the distillation tower throughsecond distillation, using a condenser so as to be recovered andsimultaneously concentrating, as a waste byproduct, thehigh-boiling-point impurities other than the stripper solventcomposition, in a bottom of the tower and the reboiler, and removingthem; and reducing an inner pressure of the distillation tower of thesecond distillation device to prevent promotion of thermal decompositionof the high-boiling-point stripper solvent.
 17. The method of claim 13,wherein the third removal step of the total stripper recyclingcomprises: transporting the stripper solvent composition obtained in thesecond removal step to a distillation tower of a third distillationdevice, and then performing third distillation under a condition of atemperature of the reboiler being set to 120° C. or less; reducing aninner pressure of the distillation tower of the third distillationdevice to prevent promotion of thermal decomposition of thehigh-boiling-point stripper solvent; condensing trace water andvolatiles removed by third distillation, using a condenser, and thenre-circulating them to the first distillation device; and passing thestripper solvent, which is a high-purity recycled stripper mixturesatisfying high-purity electronic grade quality standard by removal ofthe trace water, through a 1-micron filter, and then transporting it toa storage tank.
 18. The method of claim 13, wherein the additionalstripper recycling comprises: transporting the high-boiling-pointresidue including the high-boiling-point impurities removed by thesecond removal step of the total stripper recycling, to a distillationtower of a fourth distillation device; reducing an inner pressure of thedistillation tower of the fourth distillation device to preventpromotion of thermal decomposition of the stripper solvent contained inthe high-boiling-point residue; performing fourth distillation bymaintaining a temperature of a reboiler connected to the distillationtower of the fourth distillation device to a temperature of 160° C. orless; refluxing the high-boiling-point stripper solvent condensed by thecondenser after having been volatilized from the waste byproduct in thedistillation tower of the fourth distillation device, to a top of thedistillation tower of the fourth distillation device until it satisfieshigh-purity electronic grade quality standard; and recovering thehigh-boiling-point stripper solvent satisfying the standard, passing itthrough the 1-micron filter, and transporting it to a storage tank. 19.The method of claim 18, wherein the fourth distillation of theadditional stripper recycling is optimally controlled so as to maximallyretard deposition of the photoresist resin while monitoring an extent ofviscosification of the high-boiling-point stripper solvent contained inthe high-boiling-point residue.
 20. The method of claim 18, wherein whenviscosity of the high-boiling-point stripper solvent does not exceed amaximum threshold viscosity, the waste byproduct is circulated to anupside of the reboiler of the fourth distillation device so as to make apredetermined flow in the reboiler, thereby maximally retarding adeposition time of the photoresist resin, and when the viscosity of thehigh-boiling-point stripper solvent exceeds a maximum thresholdviscosity, a flow rate of the waste byproduct fed to the reboiler isincreased, thereby lowering the viscosity of the high-boiling-pointstripper solvent.
 21. The method of claim 13, wherein the separatestripper recycling comprises: transporting the stripper solventcomposition recovered through the second removal step using the seconddistillation device and the high-boiling-point stripper solventrecovered through the additional stripper recycling, to a fifthdistillation device; separately recovering individual high-purityelectronic grade recycled stripper solvents depending on a boiling pointof each stripper solvent of the stripper solvent composition byincreasing a number of theoretical plates of a distillation tower of thefifth distillation device while a spiral stirring type column device ofthe fifth distillation device is rotated at 2,500 rpm at maximum; andpassing the recovered individual recycled stripper solvents through the1-micron filter, and respectively transporting them to individualstripper solvent storage tanks.